Combustors are commonly used in industrial and commercial operations to ignite fuel to produce combustion gases having a high temperature and pressure. For example, a typical commercial gas turbine used to generate electrical power may include an axial compressor at the front, one or more combustors around the middle, and a turbine at the rear. Ambient air may be supplied to the compressor, and rotating blades and stationary vanes in the compressor progressively impart kinetic energy to the working fluid (air) to produce a compressed working fluid at a highly energized state. The compressed working fluid exits the compressor and flows through one or more nozzles in each combustor where the compressed working fluid mixes with fuel and ignites to generate combustion gases having a high temperature and pressure. The combustion gases expand in the turbine to produce work. For example, expansion of the combustion gases in the turbine may rotate a shaft connected to a generator to produce electricity.
The fuel supplied to the combustor may be a liquid fuel, a gaseous fuel, or a combination of liquid and gaseous fuels. If the liquid and/or gaseous fuel is not evenly mixed with the compressed working fluid prior to combustion, localized hot spots may form in the combustor. The localized hot spots may increase the production of nitrous oxides in the fuel rich regions, while the fuel lean regions may increase the production of carbon monoxide and unburned hydrocarbons, all of which are undesirable exhaust emissions. In addition, the fuel rich regions may increase the chance for the flame in the combustor to flash back into the nozzles and/or become attached inside the nozzles which may damage the nozzles. Although flame flash back and flame holding may occur with any fuel, they occur more readily with high reactive fuels, such as hydrogen, that have a higher burning rate and a wider flammability range.
A variety of techniques exist to allow higher operating combustor temperatures while minimizing undesirable exhaust emissions, flash back, and flame holding. For example, water may be added to the fuel to produce an emulsion fuel that enhances combustion efficiency and reduces the peak flame temperature, and thus nitrous oxide production, in the combustor. However, the emulsion fuel inherently tends to quickly separate back into the constituent elements of fuel and water, creating variations in the flow rate and fuel-water content of emulsion fuel supplied to each nozzle. This in turn may create flame instabilities between nozzles, decrease the overall efficiency of the combustor, and increase undesirable emissions. Therefore, an improved system and method for supplying fuel to a combustor would be useful.